1. Field of the Invention
The present invention relates to an apparatus and methodology to retrain visual function in patients who have sustained damage to areas of visual processing in the brain.
2. Background Art
A longstanding belief in neurology is that visual recovery after cortical damage must either occur spontaneously (within a few months of the insult) or not at all. Therefore, therapeutic interventions have typically involved the patient's lifestyle adaptation to his visual impairment (via use of a cane or compensatory prisms to bring portions of the blind field into the view of the remaining sighted portions).
Nevertheless anecdotal reports of “visually guided” performance, such as successfully reaching and grabbing a flickering light in the dark by “blind” patients (Riddoch phenomenon) suggested the existence of unconscious visual processing even in the absence of subjective sight. Electrophysiologically, numerous topographic visual maps have been identified in the brain, only a few of which are related to conscious appreciation. Correspondingly, the presence of a VEP (visually related electrical brain response) has been documented in cases of behavioral blindness (Bodis-Wollner et al. 1977) indicating the continued visual function of these non-conscious areas.
In recent years, this phenomenon of unconscious visual processing, called “blindsight” has been investigated in both humans and animals. Human subjects were generally stroke or accident victims who lost all or a substantial portion of their visual fields. The animals had been surgically altered to eliminate all cortex associated with conscious vision.
Whereas both human and animals showed visual improvement over the course of these studies, recovery in animals was substantially greater and included discrimination of brightness, form and color location, orientation and spatial frequency (monkeys: Miller, 1979: Pasik, 1982; Humphrey & Weiskrantz, 1967). In many cases, animals were restored to visually guided behaviors such as accurately reaching for small stationary targets (Humphrey, 1970).
A major difference between human and animal work (possibly accounting for the huge difference in outcome) is the presence of feedback and active training in animals. In human work (which was more exploratory than remedial), visual stimuli were always extremely brief (generally less than the latency of an eye movement). Subjects who successfully located these stimuli were not given immediate feedback; only at the end of a testing session were they surprised to learn of their greater than chance performance.
Nevertheless, because some improvement in humans has resulted even under these stringent conditions, prior art has been developed to mimic the laboratory paradigm of simply presenting lights for the patient to detect. For example patent document No. DE-U 93 05 147 issued to Schmielau, describes a visual training device which consists of a large dome containing arrays of small light bulbs on its inner surface. These lights are illuminated according to pre-designated sequences (and at different eccentricities from a central fixation point). Although this device does allow assessment and passive training of the visual field, its practicality is limited by (1) very large size, (2) the inflexible locations/sizes of the visual stimuli (3) limitation of presenting only lights (to stimulate “on” cells in the visual system, whereas half the visual system consists of “dark” detectors). The creation of such “dark” targets is difficult to manage in a dome construction. However, it has been shown that animals trained only to find bright targets (on a dark background) did not respond consistently to dark objects on a white background (Humphrey, 1970).
Sable (U.S. Pat. Nos. 6,464,356, 7,367,671 and 7,753,524 introduced and extended the application of computer controlled visual training, arguing the advantages of smaller size, flexibility and patient interactivity. Chief features and goals of Sabel appear to have evolved to (1) mapping the visual field to distinguish visual areas of intact function from those in which vision is degraded or absent (2) the storage of this map for future use, and (3) a computer based algorithm which uses this map to ensure presentation of training targets to preselected areas. In contrast the earlier work (U.S. Pat. No. 6,464,356) is concerned mainly with presenting the target within blind areas or zones of deteriorated vision. In U.S. Pat. No. 7,367,671, visual information such as letters and/or words are simultaneously presented to the sighted field. U.S. Pat. No. 7,753,524 also concerns the portion of the field which is to be stimulated and extends the type of visual target to include colors and spiraling stimuli.
Recent evaluations of the techniques developed by Sabel (and currently marketed under the name of Nova Vision VRT™ (Visual Restoration Therapy™) Nova Vision, Boca Raton, Fla.) have raised the following criticisms:                1. Possibility that target detection involves cues from scattered light impinging upon the good field.        2. Problems of fixation and the probability that small eye movements assisted in target location.        3. No control for false positives (over-responding).        4. Testing is in the same apparatus as training, making it unclear if reported improvement is genuine or generalizes to “real life”.        5. Curiosity as to why a small brief white light should be a more effective training stimulus than the rich, complex visual world in which the patient is constantly immersed (Horton, 2005).        
As an intended improvement upon the Sabel techniques, Huxlin (U.S. Pat. No. 7,549,743) created a vision training device with the following features:                1. Use of moving stimuli, which are believed to be more effective than stationary lights in stimulating the cortical and sub-cortical cells of the visual system. Huxlin employs random dot kinematograms of which some proportion (from 0-100%) of the small dots move in the same direction.        2. Reduction in stray light cues by using dots of luminance equal to or less than the background.        3. Comparing two anopic areas, one to be trained and the other to serve as a control.        4. A discrimination task which requires the subject to indicate the direction of motion on a keyboard        5. Sequential training of successive adjacent fields. (When motion discrimination in a small area is considered to be substantially improved, an adjacent area is then selected for training).        6. In some embodiments, auditory feedback is provided to indicate a correct keyboard response.        7. In some embodiments, the target is a contrast modulated sinusoidal grating.        8. In some embodiments, the data input device includes an eye tracker.        
According to Huxlin et al., when patients attend to visual stimuli in a stationary environment, they show improved motion awareness in the blind hemifield.
Both the Sable and Huxlin techniques share the following features:
1. Selection of delimited training zones within the blind field.
2. Brief target durations (100-500 ms) to avoid errant eye movements.
3. Sessions comprising several hundred trials.
4. Patient's response indicated by a button press.
5. Absence of feedback which might aid in target detection.
When the task objective is either to map or precisely stimulate the field, the steady fixation of the prior art is crucial. Thus, Sabel and Huxlin involve ways of insuring fixation upon a specific portion of (or immediately beside) the computer screen. However, physical intimacy of the fixation point with the screen surface has the inherent drawback of restricting the spatial plane of training to the same depth as the fixation point.
In the prior art, the test stimulus is briefly presented (for approximately 500 milliseconds) and the patient either correctly responds to it or fails to respond. Moments later a new target with different parameters (location or motion) ensues. A training session involves hundreds of trials.
Thus, in the prior art, the patient indicates target detection with a button press. In Sabel, the patient's response speed is fed back to the software as an indirect measure of visual function, e.g., those test areas corresponding to an absent or delayed response are assumed to represent either blind or visually degraded field. Performance feedback is not implemented; Sabel assumes that the mere act of focusing attention upon the blind field is therapeutic.
In Huxlin, one of four keyboard buttons must be pressed to indicate the perceived direction of target motion. This assumes the process of conscious motion discrimination to be the therapeutic element. In some embodiments of Huxlin, an auditory signal serves as feedback to indicate that the correct “motion direction” key was pressed.